To assess carbon stock changes on lands in which ARD activities have taken
place, it is necessary to either spatially delineate the land over which ARD
activities have occurred and assess the stock changes therein or use a system
of remeasured sample plots including the same areas.

The language of decision 9/CP.4 (FCCC, 1998b) implies that carbon stocks need
to be measured only in 2008 and 2012 for Article 3.3 adjustments in the first
commitment period. In Article 3.4, a stock assessment in 1990 is specifically
called for. Incorporation of a D-R Rule (see Section 3.3.2.3),
however, would require an additional carbon stock assessment at a specific year
prior to 2008 to estimate the carbon stock at the specific time a parcel of
land becomes part of the ARD land. Without such a rule, incentives exist for
deforestation followed by reforestation after 1990; with the rule, a carbon
stock assessment is required for a point in time prior to the deforestation
(e.g., 1990).

Absent this rule, an assessment for Article 3.3 (under the land-based I approach)
would entail accounting for ARD land at 2008 and 2012. If the measurements do
not coincide with the endpoints of the commitment period, however, interpolation
may be required.

Section 2.4.2 describes the data requirements for assessment
of the carbon stock of a forest. The choice of scenario will not change the
data necessary for carbon stock assessments. A carbon stock-based definition
of forest implies, however, that a carbon stock assessment is required to determine
whether an ARD activity has taken place; other scenarios involve carbon stock
assessments only after the determination that land has become ARD land.

Existing forest inventory systems may not be adequate to assess stock changes
resulting from ARD activities. For example, the U.S. National Forest Inventory
uses a two-phase sampling system that determines the forest/non-forest condition
of approximately 3 million plots (using aerial photographs) in the first phase
and establishes 300,000 permanent field plots in a second phase. Although information
collected from forested field plots should be quite adequate to estimate carbon
stocks, there are insufficient data from non-forested areas to accurately assess
stocks. An example would be a plot that was forested at one field visit, during
which adequate carbon stock information was obtained. Subsequent conversion
to a non-forest condition might mean the plot is no longer visited in the field,
although it might still contain a substantial portion of the pre-conversion
carbon stock. This plot could meet the criteria for Article 3.3, yet insufficient
information would be available to assess the stock change. Similarly, application
of a definitional scenario based solely on a low percentage of forest cover
might result in inclusion of urban lands as forest. For example, an area of
non-forest land may be developed for urban use and sufficient trees planted
to exceed the minimum cover threshold. Because this land would be classified
as forest under such a scenario, its carbon stock would be eligible for Kyoto
Protocol purposes.

Most current forest inventories were developed to efficiently estimate merchantable
wood production, not biomass or carbon content. Forest inventories generally
provide estimates of main stem volume in a green condition. The use of conversion/
expansion factors enables estimation of biomass and carbon from stemwood volume.
This technique may mask significant gaps in data for some forest conditions,
which may be important depending on the scenario. For example, wood volume in
small trees and younger stands is rarely included in forest inventories, causing
difficulty in reliably estimating forest biomass. This situation applies to
any afforestation/reforestation activities involving young stands. In particular,
scenarios in which regeneration after harvest constitutes reforestation (the
FAO and Land Cover scenarios) will involve large afforestation/ reforestation
areas with young stands. For these cases, special regeneration surveys may be
required. The lack of information on the dynamics of young stands (including
soil carbon pools) is particularly critical in the first commitment period,
when the old stands in the ARD lands will be at most 23 years old.

If the forest products pool is included in the carbon stocks to be reported
under Article 3.3, a substantial body of additional data will be required, including
estimates of carbon in wood products and the fate of this carbon. This type
of data is unavailable in many countries, and collection of such data may be
costly in relation to the stock change reported.